I once had a caterpillar with a short front filament and a deep cut across its head. It behaved exactly like its "sibling" caterpillar eating, shedding, making its silk button, J hooking, forming a chrysalis and emerging as a butterly within 1/2 of the other one. But, once everything was said and done, it was missing a hind wing and could not fly. It looked perfect in every other way. I was amazed that it was so able to go through all the stages exactly like its companion, but then was deformed in the end. It didn't even have difficulting shedding its skin, but with each molt, it still had a missing filament and a deep cut.